Plasma Treatment of Low-K Surface to Improve Barrier Deposition

ABSTRACT

Methods and apparatus for processing using a remote plasma source are disclosed. The apparatus includes an outer chamber enclosing a substrate support, a remote plasma source, and a showerhead. A substrate heater can be mounted in the substrate support. A transport system moves the substrate support and is capable of positioning the substrate. The plasma system may be used to generate activated species. The activated species can be used to treat the surfaces of low-k and/or ultra low-k dielectric materials to facilitate improved deposition of diffusion barrier materials.

TECHNICAL FIELD

The present disclosure relates generally to methods and apparatuses forprocessing using a remote plasma source for surface treatment, cleaning,and layer formation.

BACKGROUND

Plasmas are widely used for a variety of treatment and layer depositiontasks in semiconductor fabrication and other thin film applications.These applications include subtractive processes such as waferprecleaning, contaminant removal, native oxide removal, photoresistremoval, plasma etching, as well as treatment processes such asoxidation, nitridation, or hydridation of a layer both during and afterformation. “Remote” plasma sources are frequently used, where the plasmais located at some distance from the surface to be treated or substrateon which a layer is being formed. The distance allows some filtering ofthe charged particles in the plasma. For example, the density ofelectrons and ions can be adjusted or removed from the generated plasma.

Logic devices are increasingly using low-k dielectric materials as theinter-metal dielectric layer in advanced circuits. The low-k dielectricmaterials may include materials that have a dielectric constant of lessthan 3.9. Logic devices typically use copper as the conductor for theinterconnections between circuits and/or circuit elements. Copper is afast diffuser and requires the use of a barrier material to retard thediffusion of the copper through the dielectric materials. The diffusionbarrier materials are typically deposited using techniques such asphysical vapor deposition (PVD), and more recently, atomic layerdeposition (ALD) has become attractive due to its ability to depositmaterials in small space dimensions. The interaction of the depositionprecursors is sensitive to the chemical species present at the surfaceof the dielectric material. In some cases, the interaction of thedeposition precursors and the surface of the dielectric material isweak. This may lead to reduced deposition during the initial cycles ofthe ALD process. Further, the interactions may vary over time, leadingto inconsistent results and poor control in a manufacturing environment.

What is needed is a system and methods that enable the repeatable andcontrollable deposition of thin films used in the manufacture ofmicroelectronic devices, such as the use of direct or remote plasmas tocondition the surface of dielectric materials present on semiconductorsurfaces prior to further processing.

SUMMARY

The following summary of the disclosure is included in order to providea basic understanding of some aspects and features of the invention.This summary is not an extensive overview of the invention and as suchit is not intended to particularly identify key or critical elements ofthe invention or to delineate the scope of the invention. Its solepurpose is to present some concepts of the invention in a simplifiedform as a prelude to the more detailed description that is presentedbelow.

Methods and apparatus for processing using a plasma source for thetreatment of dielectric material surfaces are disclosed. The apparatusincludes an outer vacuum chamber enclosing a substrate support, a plasmasource (either a direct plasma or a remote plasma), and an optionalshowerhead. Other gas distribution and gas dispersal hardware may alsobe used. A substrate heater can be mounted in the substrate support. Atransport system moves the substrate support and is capable ofpositioning the substrate. The plasma source may be used to generateactivated species operable to alter the surface of dielectric materials.Further, the plasma source may be used to generate activated speciesoperable to provide a passivation of the dielectric material surface.

BRIEF DESCRIPTION OF THE DRAWINGS

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The drawings are not to scale and the relative dimensionsof various elements in the drawings are depicted schematically and notnecessarily to scale.

The techniques of the present invention can readily be understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a cross-sectional schematic diagram of a typicalsemiconductor device.

FIG. 2 illustrates a schematic diagram for plasma surface treatmentaccording to some embodiments.

FIG. 3 illustrates a processing system enabling plasma surface treatmentaccording to some embodiments.

FIG. 4 illustrates a flow chart of a method according to someembodiments.

FIGS. 5A-5C illustrate schematic diagrams for plasma surface treatmentaccording to some embodiments.

FIG. 6 provides a table of process parameters according to someembodiments.

FIG. 7 presents FTIR data of absorbance versus wavenumber for low-kfilms treated according to some embodiments.

FIG. 8 presents FTIR data of absorbance versus wavenumber for low-kfilms treated according to some embodiments.

FIG. 9 presents a data for XRF counts versus number of cycles as anillustration of nucleation delay according to some embodiments.

FIG. 10 presents a data for XRF counts versus number of cycles as anillustration of nucleation delay according to some embodiments.

DETAILED DESCRIPTION

A detailed description of one or more embodiments is provided belowalong with accompanying figures. The detailed description is provided inconnection with such embodiments, but is not limited to any particularexample. The scope is limited only by the claims and numerousalternatives, modifications, and equivalents are encompassed. Numerousspecific details are set forth in the following description in order toprovide a thorough understanding. These details are provided for thepurpose of example and the described techniques may be practicedaccording to the claims without some or all of these specific details.For the purpose of clarity, technical material that is known in thetechnical fields related to the embodiments has not been described indetail to avoid unnecessarily obscuring the description.

Before various embodiments are described in detail, it is to beunderstood that unless otherwise indicated, this invention is notlimited to specific layer compositions or surface treatments. It is alsoto be understood that the terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to limit thescope of the present invention.

It must be noted that as used herein and in the claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly dictates otherwise. Thus, for example, reference to “a layer”includes two or more layers, and so forth.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range, and any other stated or intervening value in thatstated range, is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges, and are also encompassed within the invention, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention. Theterm “about” generally refers to ±10% of a stated value.

The term “site-isolated” as used herein refers to providing distinctprocessing conditions, such as controlled temperature, flow rates,chamber pressure, processing time, plasma composition, and plasmaenergies. Site isolation may provide complete isolation between regionsor relative isolation between regions. Preferably, the relativeisolation is sufficient to provide a control over processing conditionswithin ±10%, within ±5%, within ±2%, within ±1%, or within ±0.1% of thetarget conditions. Where one region is processed at a time, adjacentregions are generally protected from any exposure that would alter thesubstrate surface in a measurable way.

The term “site-isolated region” is used herein to refer to a localizedarea on a substrate which is, was, or is intended to be used forprocessing or formation of a selected material. The region can includeone region and/or a series of regular or periodic regions predefined onthe substrate. The region may have any convenient shape, e.g., circular,rectangular, elliptical, wedge-shaped, etc. In the semiconductor field,a region may be, for example, a test structure, single die, multipledies, portion of a die, other defined portion of substrate, or anundefined area of a substrate, e.g., blanket substrate which is definedthrough the processing.

The term “substrate” as used herein may refer to any workpiece on whichformation or treatment of material layers is desired. Substrates mayinclude, without limitation, silicon, germanium, silicon-germaniumalloys, gallium arsenide, indium gallium arsenide, indium galliumantimonide, silica, sapphire, zinc oxide, silicon carbide, aluminumnitride, Spinel, coated silicon, silicon on oxide, silicon carbide onoxide, glass, gallium nitride, indium nitride, and combinations (oralloys) thereof. The term “substrate” or “wafer” may be usedinterchangeably herein. Semiconductor wafer shapes and sizes can varyand include commonly used round wafers of 50 mm, 100 mm, 150 mm, 200 mm,300 mm, or 450 mm in diameter.

The term “remote plasma source” as used herein refers to a plasma (e.g.,a radio frequency (RF), microwave, direct current (DC), or pulsed DCgenerated plasma) located at a distance from a deposition or treatmentlocation sufficient to allow some filtering of the plasma components.For example, the density of ions and electrons can be adjusted bydistance, and electrons and ions can also be filtered out using suitableelectrode configurations, such as a grounded metal showerhead so thatonly atomic or molecular radicals reach the substrate.

The terms “low-k”, “low-k material”, “low-k layer”, and “low-k film”will be understood to be equivalent, will be used interchangeablyherein, and will be understood to describe materials, layers, or filmsthat exhibit a dielectric constant (k) that is lower than silicondioxide (i.e. SiO₂ has a k value of 3.9).

The terms “ultra low-k”, “ultra low-k material”, “ultra low-k layer”,and “ultra low-k film” will be understood to be equivalent, will be usedinterchangeably herein, and will be understood to describe materials,layers, or films that exhibit a dielectric constant (k) that is lowerthan 2.5.

The term “inter-metal dielectric, abbreviated as (IMD)” will beunderstood to describe the dielectric material used to separate metalconductors (e.g. portions of one or more interconnect structures) withinthe microelectronic device and/or circuit.

The term “nucleation delay” will be understood to describe the number ofinitial cycles during an atomic layer deposition process whereessentially no material is deposited. The nucleation delay is determinedby fitting a straight line through data representing film thickness (ora film thickness surrogate measurement such as XRF counts) versus numberof cycles. The nucleation delay is the point where the fitted linecrosses the x-axis.

Those skilled in the art will appreciate that each of the layersdiscussed herein may be formed using any common formation technique suchas atomic layer deposition (ALD), plasma enhanced atomic layerdeposition (PE-ALD), atomic vapor deposition (AVD), ultraviolet assistedatomic layer deposition (UV-ALD), chemical vapor deposition (CVD),plasma enhanced chemical vapor deposition (PECVD), or physical vapordeposition (PVD). Generally, because of the complex morphology of thedevice interconnect structure, ALD, PE-ALD, AVD, or CVD are preferredmethods of formation. However, any of these techniques are suitable forforming each of the various layers discussed herein. Those skilled inthe art will appreciate that the teachings described herein are notlimited by the technology used for the deposition process.

Insulating materials (e.g. dielectric materials) are used inmicroelectronic circuits to separate the conducting materials (e.g.interconnect lines and transistors) from each other to preventunintended short circuits. As the transistors and circuits continue toscale to smaller dimensions, the space between the conducting materialsalso continues to shrink. Under these conditions, charge accumulateswithin the dielectric material and issues such as crosstalk, signaldelay, and heat dissipation become an issue for circuit designers.Traditionally, silicon dioxide has been used as the dielectric material.Those having skill in the art will remember that silicon dioxide has adielectric constant (i.e. k value) of 3.9. Replacing the silicon dioxidewith dielectric materials having a lower k value (e.g. low-k materials)will reduce the issues associated with crosstalk, signal delay, and heatdissipation. Further, replacing the silicon dioxide with dielectricmaterials having a very low k value (e.g. k<2.5, so-called “ultra low-k”materials) will further reduce the issues associated with crosstalk,signal delay, and heat dissipation.

Copper (and its alloys) has been adopted as the primary conductor foruse in microelectronic circuits. Copper is a fast diffusing speciesthrough most dielectric materials. Therefore, the copper conductors aretypically encased in materials that are effective as diffusion barriersthat act to retard the diffusion of the copper. Conductive metal nitridematerials are examples of materials that are effective diffusionbarriers to copper. Examples of conductive metal nitride materialsinclude titanium nitride, tantalum nitride, titanium aluminum nitride,titanium silicon nitride, tantalum aluminum nitride, tantalum siliconnitride, tungsten nitride, and molybdenum nitride, among others.

A brief description of semiconductor device examples is presented belowto provide better understanding of various plasma surface treatments.Specifically, FIG. 1 illustrates a schematic representation of substrateportions including MOS device, 100, in accordance with some embodiments.The references below are made to positive metal-oxide semiconductor(PMOS) devices but other types of MOS devices can be used in thedescribed processes and will be understood by one having ordinary skillin the art. MOS device 100 includes a p-doped substrate, 101, and ann-doped well, 102, disposed within substrate, 101. Substrate, 101, istypically a part of an overall wafer that may include other devices.Some of these devices may include silicon nitride, silicon oxide,polysilicon, or titanium nitride structures. P-doped substrate, 101, mayinclude any suitable p-type dopants, such as boron and indium, and maybe formed by any suitable technique. N-doped well, 102, may include anysuitable n-type dopants, such as phosphorus and arsenic, and may beformed by any suitable technique. For example, n-doped well, 102, may beformed by doping substrate, 101, by ion implantation, for example.

MOS device, 100, also includes a conductive gate electrode, 112, that isseparated from n-doped well, 102, by gate dielectric, 117. Gateelectrode, 112, may include any suitable conductive material. In someembodiments, gate electrode, 112, may comprise polysilicon. In someembodiments, gate electrode, 112, may include polysilicon doped with ap-type dopant, such as boron. Gate dielectric, 117, is formed from ahigh-k material (e.g. hafnium oxide). Other dielectric materials includezirconium oxide or aluminum oxide. Typically, a semiconductor materialwith high mobility such as germanium or a silicon-germanium alloy (notshown) is formed beneath the gate dielectric.

MOS device, 100, also includes p-doped source region, 104, and drainregion, 106, (or simply the source and drain) disposed in n-doped well,102. Source, 104, and drain, 106, are located on each side of gateelectrode, 112, forming channel, 108, within n-doped well, 102. Source,104, and drain, 106, may include a p-type dopant, such as boron. Source,104, and drain, 106, may be formed by ion implantation. After formingsource, 104, and drain, 106, MOS device, 100, may be subjected to anannealing and/or thermal activation process.

In some embodiments, source, 104, drain, 106, and gate electrode, 112,are covered with a layer of self-aligned silicide portions, 114, whichmay be also referred to as salicide portions or simply salicides. Forexample, a layer of cobalt may be deposited as a blanket layer and thenthermally treated to form these silicide portions, 114. Other suitablematerials include nickel and other refractory metals, such as tungsten,titanium, platinum, and palladium. After forming the blanket layer fromthe suitable metal, the layer is subjected to rapid thermal process(RTP) to react the metal with silicon contained within gate electrode,112, as well as within source, 104, and drain, 106, to form a metalsilicide. The RTP process may be performed at 700° C. to 1000° C.

MOS device, 100, may also include shallow trench isolation (STI)structures, 110, disposed on both sides of source, 104, and drain, 106.STI structures, 110, may include liners formed on the side and bottomwalls by, for example, thermal oxidation of silicon of n-doped well,102. The main body of STI structures is formed by filling a trenchwithin n-doped well, 102, with a dielectric material, such as siliconoxide. Silicon oxide may be filled using high density plasma (HDP)deposition process.

As shown in FIG. 1, gate dielectric, 117, may protrude beyond gateelectrode, 112. As such, gate dielectric, 117, may need to be partiallyetched such that it does not extend past electrode, 112, and does notinterfere with subsequent formation of liners and spacers on sidewallsof gate electrode, 112.

In some embodiments, the gate dielectric, 117, and/or the gateelectrode, 112, may receive a surface plasma treatment to improve theperformance of the device.

FIG. 2 illustrates the overall layout of some embodiments of a systemenabling combinatorial processing using a remote plasma source. Adiscussion of the system may be found in co-owned U.S. patentapplication Ser. No. 13/328,129 filed on Dec. 16, 2011 which is hereinincorporated by reference for all purposes. Portions of the '129application are included herein to enhance the understanding of thepresent disclosure. A process chamber, 200, is provided. A remote plasmasource, 202, is mounted on a chamber lid, 204, either directly asillustrated or through a short flange. The plasma, 206, is entrainedinto a central gas flow, 208, which is directed toward a showerhead,210. The showerhead is disposed within the processing chamber betweenthe remote plasma source and the substrate and is in close proximity tothe substrate, 212. The showerhead further includes multiple regions,each region containing an inert gas port. The showerhead is operable toprovide exposure of reactive species from the remote plasma source toregions of the substrate. A substrate positioning system, 214, canposition the substrate, 212, directly under the showerhead, 210. Asillustrated in FIG. 2, the substrate positioning system can provide twodisplaced axes of rotation, 216, and 218. The two-axis rotationconfiguration illustrated can provide 360° of rotation for the upperrotation (providing an angular coordinate) and 60° of rotation for thelower axis (approximating a radial coordinate) to provide all possiblesubstrate positions. Alternatively, other positioning systems such asX-Y translators can also be used. In addition, substrate support, 222,may move in a vertical direction. It should be appreciated that therotation and movement in the vertical direction may be achieved throughknown drive mechanisms which include magnetic drives, linear drives,worm screws, lead screws, a differentially pumped rotary feed throughdrive, etc.

The substrate support, 222, can include a substrate heater (e.g.,resistive or inductive) and can be sized to be larger than the largestsubstrate to be processed. Substrate temperatures for most remote plasmaapplications are less than 500 C, although any suitable heater power andrange of temperature control. The substrate support, 222, can also beconfigured to provide a gas purge flow, 224, for example from the edgesof the support, using argon, helium, or any other gas that is notreactive under the process conditions.

FIG. 3 is a simplified schematic diagram illustrating an integratedprocessing system in accordance with some embodiments of the invention.The processing system includes a frame, 300, supporting a plurality ofprocessing modules. It will be appreciated that frame, 300, may be aunitary frame in accordance with some embodiments. In some embodiments,the environment within frame, 300, is controlled. A load lock, 302,provides access into the plurality of modules of the processing system.A robot, 314, provides for the movement of substrates (and masks)between the modules and for the movement into and out of the load lock,302. Modules, 304-312, may be any set of modules and preferably includeone or more processing modules. For example, module, 304, may be anorientation/degassing module, module, 306, may be a clean module, eitherplasma or non-plasma based, modules, 308, and/or 310, may be dualpurpose modules. Module, 312, may provide conventional clean or degas asnecessary.

Any type of chamber or combination of chambers may be implemented andthe description herein is merely illustrative of one possiblecombination and not meant to limit the potential chamber or processesthat can be supported to combine combinatorial processing orcombinatorial plus conventional processing of a substrate or wafer. Insome embodiments, a centralized controller, i.e., computing device, 316,may control the processes of the processing system. Further details ofone possible processing system are described in U.S. application Ser.Nos. 11/672,478 and 11/672,473, the entire disclosures of which areherein incorporated by reference. In a processing system, a plurality ofmethods may be employed to deposit material upon a substrate.

Plasmas are widely used for a variety of treatment and layer depositiontasks in semiconductor fabrication. These applications includesubtractive processes such as wafer precleaning, contaminant removal,native oxide removal, photoresist removal, as well as treatmentprocesses such as oxidation, nitridation, or hydridation of a layer bothduring and after formation. “Remote” plasma sources are frequently used,where the plasma is located at some distance from the surface to betreated or substrate on which a layer is to be formed. The distanceallows some adjusting of the charged particles in the plasma. Forexample, the density of ions and electrons can be adjusted by distance,the electrons and ions can be removed from the generated plasma usingsuitable electrode configurations such as a grounded metal showerhead,so that, for example, only atomic radicals and molecule radicals (butnot ions) reach the substrate.

The plasma generator for a remote plasma source can use any known meansof coupling energy into atoms or molecules to ionize them and create aplasma. The energy source can be, for example, electromagnetic energysuch as microwaves, radio frequency energy, or lasers.

Typically, systems using remote plasma sources were designed to treatthe entire area of a substrate, such as a 300 mm wafer. Combinatorialprocessing is difficult and expensive when the entire area of asubstrate can only receive a single process variation. Some embodimentsof the present invention overcome this limitation by providing a remoteplasma source, an associated substrate positioning system, and a siteisolation system that allows a selected region of a substrate to beprocessed while the remaining regions of the substrate are protectedfrom exposure to the plasma and reactive radical species unless or untilsuch exposure is intended.

Accordingly, an apparatus for processing using remote plasma exposure ofa substrate is disclosed. The apparatus comprises an outer chambercontaining: a remote plasma source, a showerhead, and a transport systemcomprising a substrate support and capable of positioning the substrate.The plasma exposure process parameters can be varied. The plasmaexposure process parameters comprise one or more of source gases for theplasma generator, plasma filtering parameters, exposure time, gas flowrate, frequency, plasma generator power, plasma generation method,chamber pressure, substrate temperature, distance between plasma sourceand substrate, substrate bias voltage, or combinations thereof.

In some embodiments, methods of varying surface exposure to a plasma orreactive radical species are provided. The methods comprise exposing asubstrate to a plasma or reactive radical species from a remote plasmasource under a first set of process parameters, and exposing a substrateto a plasma or reactive radical species from a remote plasma sourceunder a second set of process parameters. The process parameters can bevaried in a combinatorial manner. Typically, the process parameterscomprise one or more of source gases for the plasma generator, plasmafiltering parameters, exposure times, gas flow rates, frequencies,plasma generator powers, plasma generation methods, chamber pressures,substrate temperatures, distances between plasma source and substrate,substrate bias voltages, or combinations thereof.

In some embodiments, a layer can be exposed to a plasma surfacetreatment, thereby altering one or more of the layer's properties.Examples of suitable atoms (e.g. radicals) include O*, N*, Cl*, F*, H*,and the like. The atoms may be used to change the surface properties ofmaterials present at the surface of the substrate. Examples of gasesthat may be used in the remote plasma source to generate the ions orreactive neutral species include H₂, H₂O, O₂, N₂, N₂O, NH₃, BCI₃, NF₃,and the like. The concentration and composition of the various speciesgenerated in the plasma may be varied by varying a number of the processparameters as well as the gas composition. A description of using theseparameters to influence the concentration and composition of the variousspecies generated in the plasma may be found in U.S. patent applicationSer. No. 14/051,287, filed on Oct. 10, 2013, and claiming priority toU.S. Provisional Application No. 61/780,128, filed on Mar. 13, 2013,each of which is herein incorporated by reference for all purposes. Andiscussion of an example of the use of hydrogen for the cleaning and/oretching of oxide layers present on the surface of a semiconductor (e.g.silicon, germanium, or silicon-germanium alloys) may be found in U.S.patent application Ser. No. 14/031,975, filed on Sep. 19, 2013, andclaiming priority to U.S. Provisional Application No. 61/779,740, filedon Mar. 13, 2013, each of which is herein incorporated by reference forall purposes.

FIG. 4 illustrates a flow chart of a method according to someembodiments. In step 402, a substrate is provided having an IMDstructure formed thereon. Typically, the IMD structure will include adielectric layer in which openings such as trenches, vias, etc. areformed. The openings will be later filled with diffusion barriermaterials and copper interconnect materials.

In step 404, the IMD structure is exposed to species generated by aplasma source. As discussed previously, the plasma source may include aremote plasma source or a direct plasma source. In some embodiments, theplasma source is a remote plasma source. The system and plasma sourcemay be employed as described earlier. The species that are generated mayinclude at least one of 0, N, CI, F, or H. Gases that may be used in theplasma source to generate the species include H₂, H₂O, O₂, N₂, N₂O, NH₃,BCI₃, or NF₃. Those skilled in the art will understand that inert gasessuch as helium, neon, argon, krypton, and xenon may also be introducedinto the plasma. Generally, these species are not active in themodification of the surface unless a bias voltage is applied to thesubstrate and ions of these inert gases are accelerated toward thesurface. In some embodiments, the species include hydrogen species oroxygen species. The hydrogen or oxygen species may be at least one ofions or neutral species. In some embodiments, the gas used to generatethe hydrogen species includes hydrogen gas. In some embodiments, the gasused to generate the oxygen species includes oxygen gas.

In some embodiments, the species react with the IMD structure present onthe surface of the substrate and effectively alter one or more of thelayer's properties. In some embodiments, the species react with the IMDstructure and form a surface that is more hydrophilic. In someembodiments, the species react with the IMD structure and passivate thesurface with chemical moieties that are more reactive toward theprecursors used to deposit subsequent layers.

In step 404, a diffusion barrier material is deposited above thedielectric material. The diffusion barrier material may be formed usingany common deposition technique such as ALD, PE-ALD, AVD, UV-ALD, CVD,PECVD, or PVD. Generally, because of the complex morphology of thedevice interconnect structure, ALD, PE-ALD, AVD, or CVD are preferredmethods of formation. In some embodiments, the deposition technique fordepositing the diffusion barrier material is ALD. Conductive metalnitride materials are examples of materials that are effective diffusionbarriers to copper. Examples of conductive metal nitride materialsinclude titanium nitride, tantalum nitride, titanium aluminum nitride,titanium silicon nitride, tantalum aluminum nitride, tantalum siliconnitride, tungsten nitride, and molybdenum nitride, among others. In someembodiments, the diffusion barrier material is tantalum nitride.

FIGS. 5A-5C illustrate schematic diagrams for plasma surface treatmentaccording to some embodiments. In FIG. 5A, a substrate, 502, is providedthat includes an IMD structure formed thereon. Those skilled in the artwill understand that the substrate may include many layers, regions, andstructures formed beneath the IMD structure. For brevity and clarity,these elements are not included (or shown) in the figures. The IMDstructure is formed of a dielectric material, 504, and openings, 506,formed therein. The openings may be trenches, vias, etc. that are wellknown in the art. In some embodiments, the dielectric material is alow-k material. In some embodiments, the dielectric material is an ultralow-k material. Typically, low-k dielectric materials and ultra low-kdielectric materials are oxide materials or carbon-based polymericmaterials. Typically, these types of materials are hydrophobic.

In FIG. 5B, the IMD structure (and the materials exposed by theopenings) is exposed to species, 508, generated by a plasma source (notshown). As discussed previously, the plasma source may include a remoteplasma source or a direct plasma source. In some embodiments, the plasmasource is a remote plasma source. The system and plasma source may beemployed as described earlier. The species that are generated mayinclude at least one of O, N, CI, F, or H. Gases that may be used in theplasma source to generate the species include at least one of H₂, H₂O,O₂, N₂, N₂O, NH₃, BCI₃, or NF₃. Those skilled in the art will understandthat inert gases such as helium, neon, argon, krypton, and xenon mayalso be introduced into the plasma. Generally, these species are notactive in the modification of the surface unless a bias voltage isapplied to the substrate and ions of these inert gases are acceleratedtoward the surface. In some embodiments, the species include hydrogenspecies or oxygen species. The hydrogen or oxygen species may be atleast one of ions or neutral species. In some embodiments, the gas usedto generate the hydrogen species includes hydrogen gas. In someembodiments, the gas used to generate the oxygen species includes oxygengas.

In some embodiments, the species react with the IMD structure present onthe surface of the substrate and effectively alter one or more of thelayer's properties. In some embodiments, the species react with the IMDstructure and form a surface that is more hydrophilic, relative to theuntreated surface. In some embodiments, the species react with the IMDstructure and passivate the surface with chemical moieties that are morereactive toward the precursors used to deposit subsequent layers.

In FIG. 5C, a diffusion barrier material, 510, is formed on the treatedsurfaces. The diffusion barrier material may be formed using any commondeposition technique such as ALD, PE-ALD, AVD, UV-ALD, CVD, PECVD, orPVD. Generally, because of the complex morphology of the deviceinterconnect structure, ALD, PE-ALD, AVD, or CVD are preferred methodsof formation. In some embodiments, the deposition technique fordepositing the diffusion barrier material is ALD. Conductive metalnitride materials are examples of materials that are effective diffusionbarriers to copper. Examples of conductive metal nitride materialsinclude titanium nitride, tantalum nitride, titanium aluminum nitride,titanium silicon nitride, tantalum aluminum nitride, tantalum siliconnitride, tungsten nitride, and molybdenum nitride, among others. In someembodiments, the diffusion barrier material is tantalum nitride.

FIG. 6 provides a table of process parameters according to someembodiments. The temperature may vary from about 25 C to about 500 C.Advantageously, the temperature is between about 100 C and about 300 C.The argon (or other inert gas) flow rate may vary between about 10 sccmand about 1000 sccm. Advantageously, the argon (or other inert gas) flowrate may vary between about 250 sccm and about 750 sccm. In someembodiments, hydrogen gas is used as the source of active species fromthe plasma. The hydrogen gas flow rate may vary from about 10 sccm toabout 100 sccm. Advantageously, the hydrogen gas flow rate may varybetween about 10 sccm and about 50 sccm. In some embodiments, oxygen gasis used as the source of active species from the plasma. The oxygen gasflow rate may vary from about 10 sccm to about 100 sccm. Advantageously,the oxygen gas flow rate may vary between about 10 sccm and about 50sccm. In some embodiments, ammonia gas is used as the source of activespecies from the plasma. The ammonia gas flow rate may vary from about10 sccm to about 100 sccm. Advantageously, the ammonia gas flow rate mayvary between about 10 sccm and about 50 sccm. In some embodiments,nitrogen trifluoride gas is used as the source of active species fromthe plasma. The nitrogen trifluoride gas flow rate may vary from about10 sccm to about 100 sccm. Advantageously, the nitrogen trifluoride gasflow rate may vary between about 10 sccm and about 50 sccm. The pressuremay vary between about 50 mTorr and about 5 Torr. Advantageously, thepressure is between about 50 mTorr and about 2 Torr. The surface may beexposed to the reactive species for times between a few seconds (e.g. 25seconds) to 60 minutes. Typically, the exposure time is on the order ofminutes. Advantageously, the exposure time is between about 5 minutesand about 40 minutes. The plasma power may vary between 200 and 2000watts. Advantageously, the plasma power may vary between 500 and 1500watts. The plasma power generation may be one of RF, DC, or pulsed DC.

In some embodiments, hydrogen was used as the active species for thetreatment of the low-k dielectric material. The process conditionsemployed an argon flow rate of between 50 and 150 sccm. The processconditions employed a hydrogen flow rate of between 10 and 30 sccm. Theprocess conditions employed a pressure of between 0.25 and 0.75 Torr.The process conditions employed an RF plasma power of between 750 and1250 Watts. The process conditions employed a substrate temperaturesetpoint of between 150 C and 210 C. The process conditions employed anexposure time of between 5 and 15 minutes.

Samples that included a low-k dielectric layer at a thickness of about3100 A were exposed to active hydrogen species generated from plasmaprocesses that covered the ranges in process parameters discussedpreviously (as used herein, “A” denotes an Angstrom unit=0.1 nm). Avariety of material and surface properties were measured before andafter the surface treatment. The thickness of the layer was monitoredusing ellipsometry. The composition of the layer was monitored usingx-ray fluorescence (XRF). The bonding of the chemical species within thelow-k dielectric layer and at the surface of the low-k dielectric layerwas monitored using attenuated total reflection-Fourier transforminfrared spectroscopy (ATR-FTIR). The hydrophobic nature of the surfaceof the low-k dielectric layer was monitored by measuring the contactangle of water droplets formed on the surface of the low-k dielectriclayer. The k value of the low-k dielectric layer was monitored bymeasuring the capacitance of the layer using a mercury probe.

The data indicated that the surface treatment using hydrogen species didnot affect the thickness of the low-k dielectric layer. The averagethickness increased from about 3141 A before the treatment to about 3153A after the treatment (˜13 A change, <1% change). The data indicate thatthe surface treatment using hydrogen species did not affect the contactangle of the low-k dielectric layer. The average contact angle increasedfrom about 40.3 degrees to about 43.2 degrees after the treatment (˜2degree change, ˜5% change). The data indicate that the surface treatmentusing hydrogen species did affect the k value of the low-k dielectriclayer. The average k value increased from about 2.37 to about 2.85 afterthe treatment (˜0.5 change in k value, ˜20% change).

FIG. 7 presents FTIR data of absorbance versus wavenumber for low-klayers treated according to some embodiments. There is asilicon-oxygen-hydrogen (e.g. Si—OH) stretch that falls between about3200 cm⁻¹ and about 3700 cm⁻¹. Exposure of an oxide surface (e.g. atypical low-k material) to active hydrogen species generated from aplasma may lead to an increase in Si—OH bonds in the near surface regionof the low-k dielectric layer. The data for the low-k dielectric layerbefore the surface treatment with active hydrogen species is illustratedwith the solid line. These data indicate almost no absorbance relativeto the background (e.g. an average value of the absorbance between about3000 cm⁻¹ and about 3200 cm⁻¹). The data for the low-k dielectric layerafter the surface treatment with active hydrogen species is illustratedwith the dashed line. These data indicate an increase in the absorbancerelative to the background (e.g. an average value of the absorbancebetween about 3000 cm⁻¹ and about 3200 cm⁻¹). These data indicate thatan increase in the number of Si—OH moieties is present at the surface ofthe low-k dielectric layer.

In some embodiments, oxygen was used as the active species for thetreatment of the low-k dielectric material. The process conditionsemployed an oxygen flow rate of between 50 and 150 sccm. The processconditions employed a pressure of between 0.05 and 0.10 Torr. Theprocess conditions employed an RF plasma power of between 500 and 1100Watts. The process conditions employed a substrate temperature setpointof between 150 C and 210 C. The process conditions employed an exposuretime of between 5 and 15 minutes.

Samples that included a low-k dielectric layer at a thickness of about3100 A were exposed to active oxygen species generated from plasmaprocesses that covered the ranges in process parameters discussedpreviously. A variety of material and surface properties were measuredbefore and after the surface treatment. The thickness of the layer wasmonitored using ellipsometry. The composition of the layer was monitoredusing x-ray fluorescence (XRF). The bonding of the chemical specieswithin the low-k dielectric layer and at the surface of the low-kdielectric layer was monitored using attenuated total reflection-Fouriertransform infrared spectroscopy (ATR-FTIR). The hydrophobic nature ofthe surface of the low-k dielectric layer was monitored by measuring thecontact angle of water droplets formed on the surface of the low-kdielectric layer. The k value of the low-k dielectric layer wasmonitored by measuring the capacitance of the layer using a mercuryprobe.

The data indicate that the surface treatment using oxygen species didnot affect the thickness of the low-k dielectric layer. The averagethickness decreased from about 3201 A before the treatment to about 3141A after the treatment (˜60 A change, <2% change). The data indicate thatthe surface treatment using oxygen species had a significant effect onthe contact angle of the low-k dielectric layer. The average contactangle decreased from about 40.3 degrees to about 19.4 degrees after thetreatment (˜21 degree change, ˜50% change). The data indicate that thesurface treatment using oxygen species did affect the k value of thelow-k dielectric layer. The average k value increased from about 2.36 toabout 2.80 after the treatment (˜0.5 change in k value, ˜20% change).

FIG. 8 presents FTIR data of absorbance versus wavenumber for low-klayers treated according to some embodiments. There is asilicon-oxygen-hydrogen (e.g. Si—OH) stretch that falls between about3200 cm⁻¹ and about 3700 cm⁻¹. Exposure of an oxide surface (e.g. atypical low-k material) to active oxygen species generated from a plasmamay lead to an increase in Si—OH bonds in the near surface region of thelow-k dielectric layer. The data for the low-k dielectric layer beforethe surface treatment with active hydrogen species is illustrated withthe solid line. These data indicate almost no absorbance relative to thebackground (e.g. an average value of the absorbance between about 3000cm⁻¹ and about 3200 cm⁻¹). The data for the low-k dielectric layer afterthe surface treatment with active oxygen species is illustrated with thedashed line. These data indicate an increase in the absorbance relativeto the background (e.g. an average value of the absorbance between about3000 cm⁻¹ and about 3200 cm⁻¹). These data indicate that an increase inthe number of Si—OH moieties is present at the surface of the low-kdielectric layer.

As discussed previously, a diffusion barrier layer is typicallydeposited prior to copper as part of the IMD structure. Generally,because of the complex morphology of the device interconnect structure,PVD, ALD, PE-ALD, AVD, or CVD are preferred methods of formation. Insome embodiments, the deposition technique for depositing the diffusionbarrier material is ALD. Conductive metal nitride materials are examplesof materials that are effective diffusion barriers to copper. Examplesof conductive metal nitride materials include titanium nitride, tantalumnitride, titanium aluminum nitride, titanium silicon nitride, tantalumaluminum nitride, tantalum silicon nitride, tungsten nitride, andmolybdenum nitride, among others. In some embodiments, the diffusionbarrier material is tantalum nitride.

In the first step of the ALD deposition of the diffusion barriermaterial, the surface is exposed to a metal precursor molecule.Typically, the metal precursor molecule is an organometallic molecule.The metal precursor molecules are delivered into the reaction chamber asa pulse and allowed to interact with the substrate. The metal precursormolecules must react with active sites on the surface of the dielectriclayer that forms part of the IMD structure to lead to deposition. Thecoverage of the metal precursor molecules on the surface may be lessthan 100% (e.g. the effective thickness of the deposited layer may beless than one monolayer). The lack of 100% coverage may be due to someof the active sites being blocked by other species, steric hindrancebetween the ligands of neighboring metal precursor molecules, or otherreasons. In the next step of the ALD deposition, excess and/or unreactedmetal precursor molecules are purged from the reaction chamber using anonreactive gas (e.g. argon, helium, nitrogen, etc.). In the next stepof the ALD deposition, the surface is exposed to a reactive gas (e.g. anoxidant, reductant, nitriding agent, etc.). The reactive gas must reactwith the adsorbed metal precursor molecules to lead to deposition. Inthe next step of the ALD deposition, excess and/or unreacted reactantgas is purged from the reaction chamber using a nonreactive gas (e.g.argon, helium, nitrogen, etc.). This completes a single cycle of the ALDdeposition. This cycle may result in a deposition of material that isless than a single monolayer in thickness. This cycle can be repeated asoften as required until a desired thickness of the diffusion barrierlayer if formed.

If the thickness of the diffusion barrier layer is plotted as a functionof the number of ALD cycles, the plot should be a straight line wherethe slope gives the deposition rate (in units of A/cycle) and they-intercept should be zero. Generally, deviations from a straight lineindicate that the deposition is not self-limiting (e.g. not a true ALDdeposition) and includes a typical CVD component. Generally, if they-intercept is not zero, then there is a nucleation delay where thefirst few cycles of the ALD deposition do not lead to depositedmaterial.

Tantalum nitride diffusion barrier layers were deposited on low-kdielectric layers using ALD. A first sample included a low-k dielectricmaterial that had no surface treatment or precleaning. A second sampleincluded a low-k dielectric material that had been chemically cleanedusing a dilute hydrofluoric acid solution prior to the tantalum nitridediffusion barrier layer deposition.

FIG. 9 presents a data for XRF counts (kilo counts per second (kcps))versus number of cycles as an illustration of nucleation delay accordingto some embodiments. The XRF counts on the y-axis correspond to emissionfrom tantalum, and thus can be used as a proxy for the thickness of thelayer. For these data, 1.1 kcps correspond to about 10 A of tantalumnitride.

The data illustrated using the square symbols are for the sample withoutthe chemical precleaning treatment. These data indicate a linearrelationship with a deposition rate of about 0.0485 kcps/cycle (i.e.˜0.44 A/cycle). These data also indicate that there is a delay of about10 cycles before the deposition of the tantalum nitride begins. Thisnucleation delay may vary over time, and may lead to inconsistentresults and poor control in a manufacturing environment.

The data illustrated using the diamond symbols are for the sample withthe chemical precleaning treatment. These data indicate a linearrelationship with a deposition rate of about 0.0441 kcps/cycle (i.e.˜0.40 A/cycle). These data also indicate that there is essentially nodelay (i.e. less than 3 cycles) before the deposition of the tantalumnitride begins. This lack of a nucleation delay may lead to moreconsistent results and improved control in a manufacturing environment.These data indicate that the deposition of the diffusion barrier layercan be affected by the condition of the surface of the low-k dielectricmaterial.

Tantalum nitride diffusion barrier layers were deposited on low-kdielectric layers using ALD. A first sample included a low-k dielectricmaterial that had no surface treatment or precleaning. A second sampleincluded a low-k dielectric material that had been exposed to a hydrogenplasma pretreatment as discussed previously prior to the tantalumnitride diffusion barrier layer deposition. A third sample included alow-k dielectric material that had been exposed to an oxygen plasmapretreatment as discussed previously prior to the tantalum nitridediffusion barrier layer deposition.

FIG. 10 presents a data for XRF counts (kilo counts per second (kcps))versus number of cycles as an illustration of nucleation delay accordingto some embodiments. The XRF counts on the y-axis are used as a proxyfor the thickness of the layer. The XRF counts on the y-axis correspondto emission from tantalum. For these data, 1.1 kcps correspond to about10 A of tantalum nitride.

The data illustrated using the circle symbols are for the sample withoutthe surface treatment or precleaning. These data indicate a linearrelationship with a deposition rate of about 0.0485 kcps/cycle (i.e.˜0.44 A/cycle). These data also indicate that there is a delay of about40 cycles before the deposition of the tantalum nitride begins. Thisnucleation delay may vary over time, and may lead to inconsistentresults and poor control in a manufacturing environment.

The data illustrated using the square symbols are for the sample withthe hydrogen plasma pretreatment as discussed previously. These dataindicate a linear relationship with a deposition rate of about 0.0441kcps/cycle (i.e. ˜0.40 A/cycle). These data also indicate that there isa delay of about 15 cycles before the deposition of the tantalum nitridebegins. This reduced nucleation delay may lead to more consistentresults and improved control in a manufacturing environment. These dataindicate that the deposition of the diffusion barrier layer can beaffected by the condition of the surface of the low-k dielectricmaterial.

The data illustrated using the diamond symbols are for the sample withthe oxygen plasma pretreatment as discussed previously. These dataindicate a linear relationship with a deposition rate of about 0.0441kcps/cycle (i.e. ˜0.40 A/cycle). These data also indicate that there isa delay of about <5 cycles before the deposition of the tantalum nitridebegins. This reduced nucleation delay may lead to more consistentresults and improved control in a manufacturing environment. These dataindicate that the deposition of the diffusion barrier layer can beaffected by the condition of the surface of the low-k dielectricmaterial.

Although the foregoing examples have been described in some detail forpurposes of clarity of understanding, the invention is not limited tothe details provided. There are many alternative ways of implementingthe invention. The disclosed examples are illustrative and notrestrictive.

What is claimed:
 1. A method comprising: providing a substrate having aninter-metal dielectric layer formed thereon; exposing the inter-metaldielectric layer to activated species, wherein the activated species aregenerated using a plasma source, wherein the activated species is atleast one of O, N, CI, F, or H; and after the exposing, depositing adiffusion barrier layer on the inter-metal dielectric layer using anatomic layer deposition (ALD) process, wherein a nucleation delay forthe ALD process is less than 5 cycles.
 2. The method of claim 1, whereinthe inter-metal dielectric layer comprises at least one of a low-k layeror an ultra low-k layer.
 3. The method of claim 1, wherein a gas used togenerate the activated species comprises at least one of H₂, H₂O, O₂,N₂, N₂O, NH₃, BCl₃, or NF₃.
 4. The method of claim 1, wherein theactivated species comprises H.
 5. The method of claim 4, wherein a gasused to generate the activated H species comprises hydrogen gas.
 6. Themethod of claim 1, wherein the activated species comprises O.
 7. Themethod of claim 6, wherein a gas used to generate the activated Ospecies comprises oxygen gas.
 8. The method of claim 1, wherein theexposing is performed at a temperature between 25 C and 500 C.
 9. Themethod of claim 8, wherein the exposing is performed at a temperaturebetween 100 C and 300 C.
 10. The method of claim 1, wherein the exposingis performed in an atmosphere comprising flowing argon at a rate between10 sccm and 1000 sccm.
 11. The method of claim 10, wherein the argon isflowed at a rate between 250 sccm and 750 sccm.
 12. The method of claim1, wherein the exposing is performed in an atmosphere comprising flowingoxygen gas at a rate between 10 sccm and 500 sccm.
 13. The method ofclaim 12, wherein the oxygen gas is flowed at a rate between 50 sccm and200 sccm.
 14. The method of claim 1, wherein the exposing is performedat a pressure between 0.05 Torr and 5 Torr.
 15. The method of claim 14,wherein the exposing is performed at a pressure between 0.05 Torr and 2Torr.
 16. The method of claim 1, wherein the exposing is performed for atime between 0.25 minutes and 60 minutes.
 17. The method of claim 16,wherein the exposing is performed for a time between 5 minutes and 20minutes.
 18. A method comprising: providing a substrate having aninter-metal dielectric layer formed thereon, wherein the inter-metaldielectric layer comprises one of a low-k layer or an ultra low-k layer;exposing the inter-metal dielectric layer to activated species, whereinthe activated species are generated using a plasma source, wherein theactivated species is at least one of O, or H; after the exposing,depositing a diffusion barrier layer on the treated inter-metaldielectric layer using an atomic layer deposition (ALD) process, whereina nucleation delay for the ALD process is less than 5 cycles, whereinthe diffusion barrier layer comprises tantalum nitride.
 19. The methodof claim 18, wherein the exposing is performed for a time between 0.25minutes and 60 minutes.
 20. The method of claim 18, wherein the exposingis performed at a temperature between 100 C and 500 C.